In a semiconductor manufacturing factory, wafers as semiconductor substrates are stored in a substrate storage container (carrier), and the substrate storage container is transported to a semiconductor manufacturing apparatus. The semiconductor manufacturing apparatus includes a carry-in/carry-out block for carrying the substrate storage container into/out of the semiconductor manufacturing apparatus, and a processing block for performing processing of a wafer. Widely used as the substrate storage container is a closed-type container composed of a container body and a lid provided at the front of the container body. A number of vertically spaced-apart wafers are stored in the container body.
A transport robot having a fork for supporting the back surface of a wafer is provided in the carry-in/carry-out block. A wafer is transferred between the substrate storage container and the processing block by allowing the fork to enter/exit the substrate storage container. Before starting the operation of the semiconductor manufacturing apparatus or during adjustment of the apparatus, a worker, either visually or by using a measuring jig, obtains a parameter of a height position which serves as a benchmark upon entry of the fork into the substrate storage container. This work is called teaching. During the manufacturing of a semiconductor product, the transport robot is driven based on the parameter obtained by the work so that undue contact (interference) between a wafer and the fork does not occur upon the above-described transfer of the wafer.
There is an individual difference in the shape of the substrate storage container. Some wafers stored in the substrate storage container can be warped. Deformation over time can occur in a mechanism involved with the above-described transfer of a wafer, such as the transport robot or a stage for placing the substrate storage container on it. Further, there is a possibility of the occurrence of a human error in setting of the above parameter. It is possible that due to these causes, contact between the fork and a wafer in the substrate storage container can occur when the fork moves back and forth with respect to the substrate storage container upon transfer of the wafer; and the fork can rub against the front or back surface of the wafer, thereby scratching the surface and generating particles. The longer it takes to detect such rubbing, the larger is the number of such damaged wafers with the progress of a process for manufacturing products in the semiconductor manufacturing apparatus. Quick detection of such rubbing is therefore required.
Patent document 1 describes a technique which involves providing a vibration sensor in a stage for a substrate storage container, and detecting collision of a wafer with a substrate mounting section in the substrate storage container based on the vibration acceleration or the frequency component of vibration detected by the vibration sensor. However, the above-described rubbing between a wafer and the fork is generally very weak, and cannot be detected with high accuracy by the technique of patent document 1. Further, as will be described below, a substrate storage container can vibrate due to various causes other than contact between a wafer and a fork. There is, therefore, a demand to more accurately detect rubbing between a wafer and a fork while preventing erroneous detection due to various causes.